His ballad Yesterday is one of the most covered songs in history -- but as he turns 70 on Monday, ex-Beatle Paul McCartney shows no signs of settling back to reflect on his extraordinary past.

Fresh from wowing huge crowds at Queen Elizabeth II's diamond jubilee concert and with another headline gig -- the London Olympics opening ceremony -- booked for next month, retirement looks a way off for the British legend.

"If I'm really enjoying this, why retire?" the most prolific, most commercially-successful former member of the Beatles told the British music magazine Mojo last year.

"People say to me, 'You work so hard'," added McCartney. "We don't work hard, we play music."

Between his years with the Fab Four, his work with Wings and his solo career, McCartney has written or co-written more than 50 top 10 singles.

Macca, as he is affectionately known, released his latest album Kisses on the Bottom in February, and is just finishing a world tour.

And as he bounced onto the stage and belted out a string of hits in the shadow of Buckingham Palace this month, he did not look like a man with eight grandchildren.

It may be the singer's third marriage, to US heiress Nancy Shevell in October, that has put the spring back in his step after his bitter divorce from model-turned-campaigner Heather Mills in 2008.

Mills walked away from the six-year marriage with a settlement worth £24.3 million (then $48 million, 30.8 million euros), and perhaps it comes as some reassurance to McCartney that his new bride has a tidy fortune of her own.

The Sunday Times Rich List estimates that Shevell, 51, brings £150 million to the couple's coffers, giving them a combined fortune of some £665 million.

This makes him Britain's richest performer -- but he insists he has never forgotten his roots. "Deep inside I'm still the boy from Liverpool," he has said.

Born to working-class parents in the port city in northwest England, McCartney met John Lennon at the age of 15 and the pair formed the Quarrymen, the skiffle band that eventually metamorphosed into the Beatles.

McCartney, Lennon, George Harrison and Ringo Starr would become synonymous with mobs of screaming fans, mop-top haircuts, and an image of four men strolling over London's Abbey Road at a zebra crossing.

Simply put, they were one of the most powerful cultural influences of their era. They are also the best-selling band in history, with their record label EMI estimating all-time sales of more than a billion discs and tapes.

Relentlessly imaginative, the band would develop the catchy tunes that sparked 'Beatlemania' in 1964 into an evolving sound incorporating every influence from psychedelia to country and western.

Lennon and McCartney formed one of the most celebrated songwriting partnerships of the 20th century, but their creative differences ultimately helped bring about the Beatles' break-up in 1970.

McCartney formed Wings with his first wife Linda in 1971, and used his ingenious ear for melody -- which had earlier given life to classics such as Hey Jude and Blackbird -- to rack up a decade of hits with the new group.

Linda, a renowned photographer and animal rights activist, died of breast cancer in 1998. After 29 years of marriage, McCartney described the loss as 'total heartbreak'.

But he was back late the next year with a new album, of mainly cover versions, and has continued the Beatles' experimental tradition -- a techno record and two classical works are among more than a dozen solo studio albums.

He has also famously duetted with the likes of Michael Jackson and Stevie Wonder.

Away from music, the singer has dabbled in painting, directed the film Give My Regards To Broad Street, and campaigned on causes ranging from animal rights to peace between the Israelis and Palestinians.

He has a son and four daughters -- including high-profile fashion designer Stella, and Beatrice, born to Mills in 2003.

Of the four Beatles, two have since died: Lennon when he was shot dead in New York in 1980 and Harrison from cancer in 2001.

McCartney is often mistakenly described as 'the last remaining Beatle' -- something that the oft-overlooked drummer Ringo Starr, who is also still recording, bears with good-natured amusement.

"We are good friends," Starr has said. "We're the only two who've experienced all this who are still here."